It is known in the art to apparently dissolve or vanish an object through the use of a partially silvered mirror, also known as transparent mirror, one-way mirror, magic mirror, or one-way glass, and by other terms. The mirror is typically set at an angle of about 45 degrees between the viewer and object. By decreasing illumination on the object while increasing illumination on the viewer's side of the mirror, the object seems to disappear. This illusion is addressed in Hayter, U.S. Pat. No. 1,900,059, which varies illumination by directing light from a single source alternately to opposite sides of the mirror, and in Weinreich, U.S. Pat. No. 5,041,044, which shows the more common method of dimming one light source while brightening a second source on the opposite side of the mirror. These inventions do not, however, address the efficient use of available illumination.
As stated above illusion devices of the type using a one-way mirror and variable illumination to vanish an object are known. Particularly where such a device is powered by batteries or where cost, size, or heat output limits illuminating power, it is important not to waste that illumination. Many different materials have been used for the "mirror" of this illusion, including smoked glass, neutral density filters, and even clear glass or plastic. The most common material is about 50% transmissive mirror comprising a glass substrate and a "silvering" of vacuum deposited metal, e.g., aluminum.
In typical mirror illusion devices, a mirror giving roughly equal transmission and reflection is used. Typically, the illumination is by sources of equal intensity behind and before the mirror. In operation (neglecting losses), 50% of the light from behind passes through the mirror to the eye of the viewer. As that light is dimmed and the light before the mirror brightens, 50% of the light before the mirror reflects to the viewer's eye. If the reflectivity of the mirror were to be increased, a savings in front illumination would result, but there would be a commensurate increase in required rear illumination. Conversely, a decrease in the reflectivity of the mirror would also require a symmetrical lighting correction.